Veggie Pot Pie with Cornmeal Pie Crust

Name: Veggie Pot Pie with Cornmeal Pie Crust
Ingredients: 1 1/4 cups all-purpose flour, plus more for the work surface; 3/4 cup white cornmeal, such as Weisenbergers; 1 teaspoon kosher salt; 1/2 cup (1 stick) unsalted butter, chilled and cut into small pieces; 1 large egg yolk; 3 to 6 tablespoons ice water; 8 small new potatoes, medium dice (about 3 cups); 1 large yam, peeled and medium dice (about 3 cups); 2 parsnips, peeled and medium dice (about 1 cup); 2 stalks celery, chopped (about 2/3 cup); 12 medium shiitake mushrooms, stems discarded and caps cut into 1/2-inch pieces (about 1 3/4 cups); 8 tablespoons vegetable oil; Salt and freshly ground black pepper; 4 tablespoons all-purpose flour; 4 cups mushroom broth, warmed; 1/2 cup frozen peas; 6 sprigs fresh thyme, leaves stripped and chopped; 1/2 sprig fresh rosemary, leaves stripped and chopped; 2 tablespoons sherry vinegar